Terriermon started out as a wild Digimon, living by the doctrine of "survival of the fittest" in the harsh realm of the Digital World. When Henry received a Digimon video game as a present from his father, he selected Terriermon to play with because he identified with him. During a battle between Terriermon and Gorillamon, Henry caused Terriermon to Digivolve into Gargomon, but Gargomon lost control of his powers and was nearly unconscious when he degenerated, encouraging Henry to regret Terriermon's digivolution. Soon after, the mysterious Blue Card was discovered among Henry's card collection. Henry swiped the card through his card reader, transforming it into a D-Power. Terriermon then Bio-Emerged into the Real World as Henry's partner. Because of Terriermon's near-death experience, Henry strongly discouraged fights, even against attacking Digimon. However, when they needed to protect a child from a rampaging Musyamon, Henry learned that there were some things worth fighting for, and eased off.

At first, Henry hid Terriermon from his family by having Terriermon act like a simple stuffed animal. Later, Terriermon met the other Tamers, and became fast friends with Guilmon (Takato's partner).

Terriermon has a laid back personality - and often uses the word "Momentai," Cantonese phrase that means "take it easy ", "Relax " or more commonly, "not a problem".

Terriermon was the first digimon to digivolve into champion level in Digimon Tamers (though this was accidental due to the situation).

In Dimensions, Terriermon has demonstrated that he has yet to learn tact and that his hacking and programming skill rivals that of his tamer. In his spare time, he prepared a program that would give digimon genders and this program was later used because of Yggsdrasil's destruction. His program ended up allowing two digimon to form a digi-egg (he got a few details wrong about reproduction).

A large amount of his time that is not spent on messing with the computers or other trouble is spent keeping his serious-minded partner grounded. While Henry is suffering from doubts concerning being an Angel, Terriermon is there to cheer him up and remind him to "momentai."

Currently, he seems to have a crush on DarkRenamon. If he'll ever act on this emotion, it is yet to be seen.

Attacks

Bunny Blast (Blazing Fire): Terriermon fires energy blasts from his mouth. This can be in either a rapid round of tiny blasts, or in one large concentrated blast.

Terrier Tornado (Petit Twister): Terriermon spins himself around and shoots a green tornado at his enemies.